"The Scarlet Letter" by Nathaniel Hawthorne, published in 1850, is considered protofeminist as the story features feminist themes before the concept of feminism was known. The concept of feminism was not known prior to the 20th century.
"The Scarlet Letter" features a female protagonist, Hester Prynne, a Puritan woman who commits adultery and become ostracised by her community. When she does not reveal who the father of her child is, she is publicly shamed and forced to wear a red "A" on her clothing as a symbol of adultery. This work is considered protofeminist as Hester struggles to overcome the hypocritical patriarchy that punished women for the crime of adultery but not men.